Tuesday, January 8, 2013

Right sizing my VM's on the VHOST

Or in other words... how many VM's can I get on my Vhosts

Hardware requirements are 64bit/x64 CPU(s) and the ability to enable virtualization in the BIOS.
Excellent post on minimum server hardware requirements for Windows Free Core Server.

Rule of thumb is the leave at least 4GB RAM for the base Windows OS.
So if I have Windows server with 64GB RAM and dual hex(6) core processors for a toal of 12 CPU's.

I have 60GBb RAM to divide amongst my VM's, I should not* over subscribe my RAM but I can over subscribe the CPU's.
Over subscribing the CPU is not as big as deal as the RAM, because the CPU's will round robin, meaning when a process is free another takes its place because you have subscribed your VM to a set of vCPUs, but not been exclusivily assigned a set of vCPU's. While on the other hand your VM can be exclusivly assigned a RAM amount.
* With Hyper-3.0 there is the ability to set a range of RAM so you can squeeze more VM's on a VHOST, but that is another blog post.

So lets say I have a standard VM's setup of:
50GB Boot volume

On the vhost server describe above I can run.
30 VM's

However keep in mind we have not discussed Hard Drive space requirements.
For the Windows Free Core Server base OS you need 100gb of space.
Thus 50gbx30VM's=1.5TB =100gb = 1.6Tb of data storage minimmum.
You want redundantcy so make it RAID 10.

Remember this is just an example you need to do the math for what makes the best sense for your needs, just do not exceed your hardware, RAM and diskspace, keeping in mind the requirement needs of the base OS.

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